System and method for determining a concentration of a gas in a container

ABSTRACT

A system and method for measuring a concentration of a gas in a container having at least one flexible or variable side or wall. The system and method comprising creating a determinable optical path length through the container having a shape. Positioning a light source head and a detector head against at least one of the least one flexible or variable side or wall. Transmitting a light signal between the light source head and the detector head through the determinable optical path length. Determining the concentration of the gas in the container based on detected light and the determinable optical path length.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/891,956 filed Nov. 17, 2015 entitled System And Method ForDetermining A Concentration Of A Gas In A Container, which is a U.S.National Phase of International Patent Application No.PCT/EP2014/061001, International Filing Date May 27, 2014 entitledSystem And Method For Determining A Concentration Of A Gas In AContainer, which claims benefit of Swedish Patent Application No.SE1350641-5, filed May 27, 2013 entitled System And Method ForDetermining A Concentration Of A Gas In A Container and Swedish PatentApplication No. SE1350640-7, filed May 27, 2013 entitled System AndMethod For Determining A Concentration Of A Gas In A Container; all ofwhich are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

This disclosure pertains in general to determine a concentration ofgaseous content in a container with non-well defined outer geometry.More particularly the disclosure relates to gas absorption spectroscopyof gaseous content in a container. Especially the disclosure relates todetermining or calibrate for an optical path length in containers withat least one flexible or variable wall which is optically transparent ortranslucent.

Background of the Disclosure

Optical absorption spectroscopy is an established method to measuregaseous species inside containers, in a non-invasive and non-destructivemanner. In traditional analysis, the procedure requires that the opticalpath length in the volume containing the gaseous species to be measuredis well defined, which can be accomplished e.g. by using special purposecontainers (vials) with optical grade transparent walls and knowndistance between the walls. However, there is a great need in certainapplications to be able to monitor or quantify the gases insidecontainers that have not been designed for the purpose of spectroscopicmeasurements. Examples of such applications include packages offoodstuffs that utilize modified atmosphere packaging (MAP) to prolongor ensure longevity. Such packages are normally not designed withspectroscopic analysis in mind and may be made of flexible or softmaterials. It is desired to measure the gaseous content of suchcontainers for the purposes of process control and quality control.Similar applications exist in the areas of packaging of pharmaceuticalsand other medical products. Such measurements may be carried out eithermanually or in an automated manner in a production or transportlogistics line.

Hence, new improved apparatus and methods for determining an opticalpath length in such containers would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, examples of the present disclosure preferably seek tomitigate, alleviate or eliminate one or more deficiencies, disadvantagesor issues in the art, such as the above-identified, singly or in anycombination by providing a device, system or method according to theappended patent claims for determining an optical path length incontainers with flexible or variable and optically transparent ortranslucent walls.

Herein a container may be either a container having at least oneflexible wall or a container with an unpredictable path length due to,for example, the content. Examples of such containers but not limited toare, flexible bags, e.g. bags made of plastic, or a tray with, forexample, a covering cling films or plastic wrap, trays made ofsemi-rigid or rigid plastic used for food stuff.

In a first aspect a method of determining a concentration of a gas in acontainer having at least one flexible or variable side or wall isdisclosed. The method comprising creating a determinable optical pathlength through said container having a shape.

Some technique disclosed herein for creating a determinable optical pathlength pertains to modify the shape of the flexible or semi-rigidcontainer. By modify the shape of the container, a fixed optical pathlength may be provided between two points. The optical path length maythen be established either from the fixed distance obtained between thewalls of the modified container or indirectly as part of determining theconcentration of the gaseous content using a calibration routine.

Absorption signals are recorded or obtained by transmitting a lightsignal between a light source head and a detector head through thedeterminable optical path length. Determining the concentration of gasin the container based on detected light and the determinable opticalpath length.

The absorption signal may be a full absorption spectrum or a signal fromat least one discrete wavelength.

In some examples of the disclosure, the method comprises modifying theshape of the container for the creating the determinable optical pathlength through the container having a shape.

Some examples of the disclosure, further comprises positioning a lightsource head and a detector head against at least one of the least oneflexible or variable side or wall.

Positioning the light head and detector head may be done simultaneouslyas the shape of the container is modified or subsequent to themodification of the shape.

After the shape has been modified a fixed and determinable optical pathlength is obtained between at least two walls or sides of the container.The optical path length may then be established. Alternatively, sincethe optical path length for the same type of container may be repeatablefixed the same distance, the measurement conditions are traceable.Hence, instead of directly determining the optical path length throughthe container, a calibration routine may be performed. The calibrationroutine may include measuring one or more similar containers with aknown concentration of the gas and where the optical path length hasbeen created and fixed to the same distance as the optical path lengthof the container with an unknown concentration of the gas.

In some examples of the disclosure, the modifying the shape of thecontainer includes pulling at least one side or wall a distance relativeat least one second side or wall by using at least one movable temporaryattachment point, such as at least two movable temporary attachmentpoints, thereby creating the determinable optical path length throughthe container.

In some examples of the disclosure, the method comprises, moving onemovable temporary attachment point, such as at least two movabletemporary attachment points, towards said container; and temporarilyattaching at least one wall or side to the movable temporary attachmentpoint, thereby creating the determinable optical path length through thecontainer.

In some examples of the disclosure, the method comprises modifying theshape of the container by pushing at least one side or wall a distancetowards at least one second side or wall at one location therebyinflating the container at a second location creating the determinableoptical path length through the container at the second location.

In some examples of the disclosure, the method comprises moving thelight source head and/or detector head towards at least one wall or sideof the container, and detecting when the light source head and/ordetector head is in contact with the walls or sides of the container.The distance between the light source head and the detector head iscreating the determinable optical path length through the container.

Alternatively, the distance between the light source head and thedetector head at one side and a reflector at the opposite side of thecontainer is creating the determinable optical path length through thecontainer.

In some examples of the disclosure, modifying the shape of the containercomprises positioning the container in an enclosure having walls andthereafter at least partly evacuating an atmosphere of the enclosure.The evacuation is expanding the container so that the walls or sides ofthe container make contact with the walls of the enclosure and therebycreating the determinable optical path length through the container.

In some examples of the disclosure, the method comprises positioning thelight source head and the detector head at opposite sides of saiddeterminable optical path length. The method may alternatively comprise,positioning the light source head and the detector head at the same sideof the determinable optical path length and a reflective means at anopposite side.

In some examples of the disclosure, the method comprises utilizing acalibration routine based on using two laser beams, instead ofdetermining said determinable optical path length.

Alternatively, the method may comprise a calibration routine based onmeasurements on a second container having a known gas concentration anda determinable optical path length equal to the determinable opticalpath length of the container with an unknown gas concentration.

In some examples of the method, the container is a tray with a flexibleprotection layer, such as a film, that is at least partly transparent.The method comprises pushing down the flexible protection layer by amechanical means and a light signal is transmitted at an angle by thelight source through the flexible protection layer of the tray andthrough a headspace and at a sidewall of the tray, detecting signal areflected by the sidewall or transmitted through the sidewall.

In a further aspect, a system for measuring a concentration of a gas ina container having at least one flexible or variable side or wall isdisclosed. The system comprises a light source head and a detector head.The system may further comprise means for making contact between anexterior of the walls or sides of the container, thereby creating adeterminable optical path length through the container when contact ismade. The system may also comprise a control unit for determining theconcentration of a gas in a container based on detected light and thedetermined optical path length upon the contact.

In some examples of the disclosure, the means is at least one movabletemporary attachment point to be attached to the exterior of the wallsor sides of the container for pulling at least one side or wall of thecontainer a distance relative at least one second side or wall to createthe determinable optical path length through the container.

In some examples of the disclosure, the means are mechanical fixturesfor pushing at least one side or wall of the container a distancetowards at least one second side or wall at one location. The pushing ata first location may inflate the container at a second location, thuscreating the determinable optical path length through the container atthe second location upon the pushing.

In some examples of the disclosure, the means are movable to positionthe light source head and/or detector head in contact with at least onewall or side of the container. Further, the means comprises a sensor fordetecting when the light source head and/or detector head is in contactwith at least one wall or side of the container, thereby creating thedeterminable optical path length through the container.

In some examples of the disclosure, the means is an enclosure configuredfor the container to be positioned in. The means comprises a unit for atleast partly evacuating an atmosphere of the enclosure wherein thecontainer is expanded so that the walls or sides of the container canmake contact with the walls of the enclosure. The at least partlyevacuation of the atmosphere may create the determinable optical pathlength through the container.

In some examples of the disclosure, the light source head and thedetector head are arranged at opposite sides of the determinable opticalpath length. Alternatively, the light source head and the detector headare arranged at the same side of the determinable optical path lengthand a reflective means at an opposite side of the container.

In some examples of the disclosure, the container is a tray with aflexible protection layer, such as a film, that is at least partlytransparent. The means for making contact is a mechanical means forpushing down the flexible protection layer and the light signal istransmitted at an angle by the light source through the flexibleprotection layer of the tray and through a headspace and at a sidewallof the tray, the signal is reflected by or transmitted through thesidewall of the tray and is detected by the detector.

In some alternative examples in accordance with the disclosure, a methodof determining a concentration of at least a first gas in a containerhaving at least one flexible or variable side or wall is disclosed. Themethod comprises estimating an optical path length through thecontainer. The method further comprise transmitting a first light signalbetween a light source and detector through the estimated optical pathlength and determining the concentration of the first gas in thecontainer based on detected light of the first light signal and theoptical path length.

In some further alternative examples in accordance with the disclosure,a system of determining a concentration of at least a first gas in acontainer having at least one flexible or variable side or wall isdisclosed. The system comprises a light source and a detector fortransmitting a first light signal through the container. The devicefurther comprises a estimation unit for estimating an unknown opticalpath length that the first light signal travels through the container,and a control unit for determining the concentration of the at leastfirst gas in the container based on detected light of the first lightsignal and the optical path length estimated by the estimation unit.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which examples ofthe disclosure are capable of will be apparent and elucidated from thefollowing description of examples of the present disclosure, referencebeing made to the accompanying drawings, in which

FIG. 1 is illustrating an example of creating a determinable opticalpath length through a container by pulling the walls or sides;

FIG. 2 is illustrating an example of creating a determinable opticalpath length through a container by pushing the walls or sides;

FIG. 3 is illustrating another example of creating a determinableoptical path length through a container by pushing the walls or sides;

FIG. 4 is illustrating an example of creating a determinable opticalpath length through a container by positioning it in an evacuableenclosure;

FIG. 5 is illustrating an example of a system including a parallelchannel for measuring a second gas;

FIG. 6 is illustrating another example of a system including a parallelchannel for measuring a second gas;

FIG. 7 is illustrating reflectance measurements on a tray;

FIG. 8 is illustrating measurements on a tray using an exemplaryconfocal configuration;

FIG. 9 is illustrating measurements on a tray using another exemplaryconfocal configuration;

FIG. 10 is depicting results from an exemplary experiment of a pullingconfiguration;

FIG. 11 is depicting results from an exemplary experiment of a pushingconfiguration;

FIG. 12 is depicting results from an exemplary experiment of anauto-sensing configuration;

FIGS. 13 A and B are illustrating an exemplary gas measurementconfiguration where a light beam is directed through a top of the trayand at a sidewall of the tray at an angle; and

FIG. 14 is illustrating results from exemplary O2 measurements on atray.

DESCRIPTION OF EXAMPLES

The following disclosure focuses on examples of the present disclosureapplicable to determining an optical path length in containers withflexible or variable and optically transparent or translucent walls. Forexample, this is advantageous for determining a concentration a gas byabsorption spectroscopy of gaseous content in a container. However, itwill be appreciated that the description is not limited to thisapplication but may be applied to many other systems an optical pathlength need to be determined.

Absorption spectroscopy may either be a full absorption spectrum or asignal from at least one discrete wavelength.

It is assumed that the container that is subject to measurementcomprises of a transparent, semi-transparent or translucent material.Alternatively, the container may have a window made of a transparent,semi-transparent or translucent material, which at least partiallycovers a wall or side of the container. The container may in someexamples have two windows at opposite walls or sides.

The walls or sides of the container may either be non-rigid (flexible orsoft) or the walls may be rigid but the process is such that the opticalpath length inside the containers vary in an unpredictable mannerbetween individual containers or measurement situations. By determiningthe optical path length the light travels through the container theabsorption of a gaseous content may be calculating using, for example,Beer-Lambert law. Alternatively and/or additionally, in some examples,instead of determining the optical path length after it has been fixed,a calibration or reference may be used to obtain the concentration of agaseous content.

In an example illustrated in FIG. 1, a system 100 comprising of at leastone movable temporary attachment points 12 that is attach to thecontainer 11 during the measurement and a second fixed temporaryattachment point.

Alternatively, the system 100 may comprise at least two movabletemporary attachment points 12 at opposite sides of a determinableoptical path length to be created.

Attachment may be accomplished by, but is not limited to, suction(vacuum), adhesives, or electrostatics. An optical measurement apparatuscomprising of at least one light source head 13 and at least onedetector head 14 mounted in, on or beside the temporary attachmentpoints 12. The light source head 13 and the detector head 14 are mountedin a manner that when the distance between some given points for thetemporary attachment points 12 is known, then the distance L between thelight source head 13 and detector head 14 is also known. Further, whenthe movable temporary attachment points 12 are attached to the container11, the light source head 13 and detector head 14 will be in contactwith, or in very close vicinity to, the container walls, or with knowndistance to the walls. Prior to performing the measurement, thecontainer 11 is placed between the temporary attachment points 12, andat least one of attachment points 12 is then moved toward the container11 until a sufficient number of them make contact with the container 11.When the temporary attachment points 12 have attached to the containerwalls, the temporary attachment points 12 may mechanically be withdrawn,bringing the container walls apart, to a pre-determined optical pathlength having a distance L. When separating the walls or sides of thecontainer 11 the shape of the container 11 is modified, hence creatingan determinable optical path length having a distance L.

Alternatively, the determinable optical path length may be taken as thedistance when the temporary attachment points 12 first make contact withthe container with no further adjustments by separating the walls orsides by pushing them apart.

FIG. 1A is depicting a situation before measurement where the at leastone temporary attachment points 12 are about to attach to the container.FIG. 1B is illustrating a situation during measurement wherein thetemporary attachment points 12 are attached to container 11.

In another example, the light source head and detector head aremechanically mounted so that at least one of them can be moved in atleast one degree of freedom, allowing the light source head and thedetector head to come in close contact with the container walls.Moreover, the distance between the light source head and the detectorhead may be known, by means of but not limited to, mechanicalcalibration of the distance at all possible positions, or by some meansof electronic or optical determination of their respective positions andsuccessive calculation of the distance between them. Prior to performingthe measurement, the container is placed between the light source headand the detector head, and the light source head and/or detector headare then moved toward the container until both of them make contact withthe container. In an automated process, such as an autosensing process,there is some means to detect when the light source head and thedetector head make contact with the container wall, e.g., by means ofbut not limited to, micro switches, electrical, or optical methods.

Alternatively, in some examples the light source head and detector headis mounted at a fixed distance. Prior to measuring the container isforced in-between the light source head and detector head. The fixeddistance between the light source head and the detector head is suchthat the contained occupies substantially all of the space and the laserand detector head come in close contact with the container walls. Thusthe path length inside the container is known.

Additionally, in some examples, instead of determining the optical pathlength through the container after the optical path length has beenfixed by temporary attachment points, a calibration method as describedin relation to FIG. 5 may be used to establish the concentration of agaseous content in the container 11.

Additionally and/or alternatively, in some examples of the system 100depicted in FIG. 1, instead of directly determining the optical pathlength L inside the container 11, it is possible to obtain the gasconcentration by means of calibration. The calibration may be performedby performing measurements on one or more containers with a knownconcentration of the gas. The recorded signals obtained by the detectorcorrespond to particular gas concentrations in the container. The gasconcentration may then be subsequently determined on containers 11 withan unknown gas concentration without directly establishing the opticalpath length, as long as the measurement conditions are traceable to themeasurement conditions used during the calibration. One way ofestablishing traceable measurement conditions is to use techniquedisclosed in conjunction with FIG. 1.

In another example illustrated in FIG. 2, a system 200 comprising acontainer 21 that is subject to measurement is placed in a mechanicalfixture 22 which applies a mechanical pressure to the walls at onelocation of the container 21. The increased pressure will inflateanother second location of the container and push the container walls ofthe second location of the container 21 against the light source head 23and detector head 24. The distance L of the separated walls may bedetermined as the distance L between the light source head 23 and thedetector head 24 since this distance may be known. Because the containervolume after inflation occupies substantially all of the space betweenthe light source head 23 and detector head 24, the optical path lengthinside the container 21 may be determined.

FIG. 2A is depicting a situation before measurement where a container 21is placed between mechanical fixtures 22. FIG. 2B is depicting asituation during a measurement where container 21 is inflated bymechanical force.

The area of the mechanical fixture 22 which exerts a pressure on thecontainer 21 may be a point, clamp-like or constructed like an iris.

The container may here be a flexible bag or a semi rigid tray. A semirigid tray may, for example, be made of thin plastic which flex enoughfor the shape to be modified by exertion of an external pressure on atleast one wall of the tray.

Additionally, in some examples, instead of determining the optical pathlength through the container after the optical path length has beenfixed by temporary attachment points, a calibration method as describedin relation to FIG. 5 may be used to establish the concentration of agaseous content in the container 21.

Additionally and/or alternatively, in some examples of the system 200depicted in FIG. 2, instead of directly determining the optical pathlength L inside the container 21, it is possible to obtain the gasconcentration by means of calibration. The calibration may be performedby performing measurements on one or more containers with a knownconcentration of the gas. The recorded signals obtained by the detectorcorrespond to particular gas concentrations in the container. The gasconcentration may then be subsequently determined on containers 21 withan unknown gas concentration without directly establishing the opticalpath length, as long as the measurement conditions are traceable to themeasurement conditions used during the calibration. One way ofestablishing traceable measurement conditions is to use techniquedisclosed in conjunction with FIG. 2.

FIG. 3 illustrates a system 800 comprising a mechanical fixture 82similar to the mechanical fixture 22 in FIG. 2. The light source head 83and the detector head 84 are attached to the mechanical fixture 82. Thelight source head 83 and the detector head 84 have areas 86 configuredto be positioned against the walls of the container 81. These areas 86may either be aligned with the areas 85 of the mechanical fixture 83which are configured to exert an external pressure on the container 81.Alternatively, the areas 86 of the detector head 84 and light sourcehead 83 may be positioned a distance from the areas 85 of the mechanicalfixture 83, as illustrated in FIG. 3. In this way the areas 86 may comeinto contact with the walls of the container 81 when the increasedpressure on a first location of the container 81 inflates a secondlocation of the container. When the areas 86 are in contact with thewalls of the container 81, the optical path length L may be determined.FIG. 3A is illustrating before measurement and FIG. 3B is illustratingwhen the second location has been inflated by the exert of an externalpressure form the mechanical fixtures 82.

Additionally, in some examples, instead of determining the optical pathlength through the container after the optical path length has beenfixed by temporary attachment points, a calibration method as describedin relation to FIG. 5 may be used to establish the concentration of agaseous content in the container 81.

Additionally, in some examples, instead of determining the optical pathlength through the container after the optical path length has beenfixed by temporary attachment points, a calibration method as describedin relation to FIG. 5 may be used to establish the concentration of agaseous content in the container 81.

Additionally and/or alternatively, in some examples of the system 800depicted in FIG. 3, instead of directly determining the optical pathlength L inside the container 81, it is possible to obtain the gasconcentration by means of calibration. The calibration may be performedby performing measurements on one or more containers with a knownconcentration of the gas. The recorded signals obtained by the detectorcorrespond to particular gas concentrations in the container. The gasconcentration may then be subsequently determined on containers 81 withan unknown gas concentration without directly establishing the opticalpath length, as long as the measurement conditions are traceable to themeasurement conditions used during the calibration. One way ofestablishing traceable measurement conditions is to use techniquedisclosed in conjunction with FIG. 3.

In FIG. 4, a system 300 comprising a container 31 that is subject tomeasurement is illustrated. The container 31 is placed inside anenclosure 32 surrounded by walls in a plurality, but not necessarilyall, spatial directions. The light source head 33 and the detector head34 are placed at least one of the walls of the enclosure 32. Prior toperforming the measurement, the atmosphere in the enclosure 32 is atleast partly evacuated, creating an at least partial vacuum inside theenclosure. The lower atmospheric pressure in the enclosure causes thevolume in the container to expand and the container walls to makecontact with the enclosure walls, and thus make contact with the lightsource head 33 and detector head 34. Since the distance L between theenclosure walls may be known, the optical path length inside thecontainer 31 may also be known in this configuration.

FIG. 4A is depicting a situation before measurements when the container31 has been placed in enclosure 32. FIG. 4B is depicting a situationafter the atmosphere in the enclosure 32 has been at least partlyevacuated.

Additionally, in some examples, instead of determining the optical pathlength through the container after the optical path length has beenfixed by temporary attachment points, a calibration method as describedin relation to FIG. 5 may be used to establish the concentration of agaseous content in the container 31.

Additionally and/or alternatively, in some examples of the system 300depicted in FIG. 4, instead of directly determining the optical pathlength L inside the container 31, it is possible to obtain the gasconcentration by means of calibration. The calibration may be performedby performing measurements on one or more containers with a knownconcentration of the gas. The recorded signals obtained by the detectorcorrespond to particular gas concentrations in the container. The gasconcentration may then be subsequently determined on containers 31 withan unknown gas concentration without directly establishing the opticalpath length, as long as the measurement conditions are traceable to themeasurement conditions used during the calibration. One way ofestablishing traceable measurement conditions is to use techniquedisclosed in conjunction with FIG. 4.

Alternatively, in the examples illustrated and disclosed in relation toFIGS. 1 to 4, the light source head and the detector head may be placedat the same location and a reflective surface at the opposite side ofthe container. In such a configuration the light will be reflected backby the reflective surface and the light will travel a distance of twicethe optical path length. Hence the accuracy of the measuredconcentration may increase.

In another example, the light source head and detector head are mountedin a fixed configuration and the container, such as a bag or a tray,subject to measurement is placed in between or in front of to the lightsource head and detector head and a gas-probing light beam is sentthrough the container. Alternatively the gas probing beam is sentthrough the container and is reflected back. Alternatively of having thelight beam travelling through the container is to reflect the light beamagainst a, for the light, reflective surface inside the container. Thereflective surface may be an inner surface of the container itself.

The unknown distance the light beam travels through the container may bemeasured with the help of wall localization using an imaging systemutilizing, e.g., by means of but not limited to, focus detection, spotdetection of probing laser beam or reference beam, or image analysis.The focusing detection system, rangefinder, may use, but not limited toelectroacoustic or electronic means. The imaging system can bepositioned on, but not limited to, the same side as the light sourcehead or above the container.

In another example, the light source head and detector head are mountedin a fixed configuration and the container subject to measurement isplaced in-between or in front of to the light source head and detectorhead and the gas-probing light beam is sent through the container,alternatively through and reflected back. The distance the light istravelled through the container is estimated utilizing rangingtechnologies for determining the positions of the walls of thecontainers or a reflector inside the container. Ranging methods include,e.g. but not limited to laser rangefinder with pulsed laser ortriangulation, or ultra sound eco ranging.

FIG. 5 illustrates an example of a dual channel system 400. Agas-probing light is sent by a first light source head 42 through acontainer 46 having unknown dimensions, such as an unknown optical pathlength. The light is detected by a first detector head 43 which may bepositioned opposite the first light source head 42. Alternatively, thefirst light source head 42 and the first detector head 43 may be locatedat the same side and a reflector is positioned at the opposite side.

A parallel gas-measurement channel sending light from a second lightssource head 44 to a second detector head 45 is utilized to measure thegas-probing light distance by means of absorption spectroscopy of asecond gas present in the container. This second gas has a knownconcentration, e.g. but not limited to water vapour or carbon dioxide.The second channel laser beam overlaps or at least travels a similarpath as the primary gas-sensing laser light through the container 46.Alternatively, the second light source head 44 and the second detectorhead 45 may be located at the same side with a reflector positioned atthe opposite side.

An advantage with this method is that by calibrating against the secondchannel, there is no need to determining the optical path length Lthrough the container 46.

FIG. 6 illustrates another example of a system 900 having dual channels.A first light source head 92 and a second light source head 94 ismounted opposite a first detector head 93 and a second detector head 95.The light source heads and the detector heads are mounted in a fixedconfiguration with a known distance sending a beam through, for example,an enclosure or between to walls. Alternatively, in some examples, thelight source heads and the detector heads may be mounted at the sameside and a reflector may be mounted at the opposite side.

FIG. 6A illustrates a system 900 subject to a measurement of a primarygas which concentration is to be estimated. FIG. 6B illustrates system900 with a container 96 positioned in the path of the beams. In thisexample, the second light source head 94 and the second detector head 95forms a second parallel gas-sensing channel. This second channel isconfigured to use laser absorption spectroscopy to measure at least oneadditional gas other than the primary gas. This at least one additionalgas may either not be present or at least present with a knownconcentration inside the sealed container. The at least one additionalgas should be present naturally or by choice in the surrounding of thecontainer. The difference in gas absorption of the second channel in thesystem 900 with the container 96 present or not present allows a measureof the distance the light pass through the gas inside the container. Inthis configuration, the second channel laser beam overlaps or at leasttravels a similar path as the primary gas-sensing laser light.

FIG. 7 illustrates an example of a system 1000 for measuring theconcentration of at least one gas inside a tray 1001, where the opticalpath length is unknown. A first light source and a first detector arepositioned at a location 1004 outside of the tray 1001 and a secondlight source and a second detector is positioned at a location 1005outside of the tray 1001. The first light source and the first detectorare configured for measuring a primary gas which concentration is to beestimated. The second light source and the second detector areconfigured for measuring at least one second gas with knownconcentration.

The at least one second gas, e.g. but not limited to water vapor orcarbon dioxide, has a known concentration.

The light from the first and second light source is transmitted througha wall of the tray 1001. The light may either be reflected back by thecontent 1002 in the container or by a separate reflective surfacepositioned at the surface of the content 1002.

Additionally and/or alternatively, in some examples the light from thefirst and second light source is transmitted through the wall 1001 andreflected back by a wall of the tray.

In some examples, the reflective area may be an inner surface of a sidewall of the tray. To illuminate an inner surface of the side wall and todetect back reflected light, the light beams are directed through thetop film of the tray and through the headspace, at a sidewall of thetray at an angle. The detector or detectors is arranged at an angle tocollect the light reflected back. This configuration ensures that thecontents of the package may not interfere with the light beam.

Alternatively, in some examples, depending on whether the sidewall ofthe tray is transparent or not, the detector or detectors may be used intransmission mode. In transmission mode the detector or detectors arepositioned outside of the sidewall and arranged so as to detect thelight that has been transmitted at an angle through a top surface of thetray, through the headspace and through a sidewall.

The light of the first beam and the light of the second beam may betransmitted into the tray as parallel beams, overlap in the same beampath or at least travels a similar path. If the beams overlap in thesame beam path, only one detector may be needed. If the same detector isused, the beams may be separated by modulation of the frequencies or byusing filters in front of the detector.

Since the concentration of the at least second gas is known, the opticalpath length in the tray 1001 may be determined or calibrated for. Hencethe concentration of the primary gas can be estimated.

For obtaining parallel or overlapping beam paths the configuration ofthe positions of the light sources and the detectors may be varied andcombined with further components such as partially transparent mirrorsand filters.

FIG. 8 illustrates a system 1100. A laser head 1104 and a detector head1110 are placed in a confocal configuration using a partiallytransparent mirror 1109 and a lens assembly 1106 and 1107. At thedetector 1110, there is a pinhole 1111 which suppresses light reflectingfrom points other than the confocal point. The objective lens 1107 ismovable along the direction of the optical axis. To find the opticalpath length inside the container, an automated system moves theobjective lens 1107 until a maximum signal is detected by the detector1110, which corresponds to when the objective lens 1107 is focused onthe far surface of a content 1102 or added reflective area inside thecontainer 1101. Since the working distance of the focal length of theobjective lens 1107 is known, and the distance of the objective lens1107 from the first surface 1112 of the container 1101 can be known, theoptical path length inside the container 1101 can be determined.

In some examples, the reflective area may be an inner surface of a sidewall of the tray. To illuminate an inner surface of the side wall and todetect back reflected light, the whole confocal arrangement is arrangedat an angle to emit light towards the inner surface of the sidewall andto detect light reflected back from the inner surface of the sidewall.This configuration ensures that the contents of the package will notinterfere with the light beam.

Alternatively, in an example illustrated in FIG. 9, a laser 1204illuminates the back surface of a container 1201, or the content 1202 oran added reflective area inside the container 1201. The laser 1210 isseparated from the confocal arrangement which includes a detector 1205,a pin hole 1208, a leans 1206 and a movable objective lens 1207. Theillumination is done from a well-defined position in relation to theconfocal arrangement and a first wall 1209 of the container 1201. Insome examples, the reflective area may be an inner surface of a sidewall of the tray. To illuminate an inner surface of the side wall and todetect back reflected light, the light beam is directed through the topfilm of the tray and through the headspace, at a sidewall of the tray atan angle. The confocal arrangement is also arranged at an angle todetect light reflected back from the inner surface of the sidewall. Thisconfiguration ensures that the contents of the package will notinterfere with the light beam.

The disclosure further relates to a method of determining aconcentration of at least a first gas in a container having at least oneflexible or variable side or wall, the method comprises estimating anoptical path length through the container. The method also includestransmitting a first light signal between a light source and a detectorthrough the estimated optical path length and determining theconcentration of the first gas in the container based on detected lightof the first light signal and the optical path length.

In some examples, the method comprises positioning the light source anddetector at a side of the container and a reflector arranged forreflecting the first light signal at an opposite side of the container.

In some examples, estimating the optical path length is based ontransmitting a second light signal between a second light source and thedetector for measuring absorption spectra of a second gas with a knownconcentration.

In some examples, estimating the optical path length is based ontransmitting a second light signal between a second light source and asecond detector for measuring an absorption signal of a second gas witha known concentration.

In some examples, the second gas is inside the container and/or outsidethe container.

In some examples, the second signal is transmitted the same optical pathlength as the first light signal

In some examples, the estimation of the optical path length and thetransmitting of a first light signal is performed using a confocalconfiguration.

In some examples, estimating the optical path length through thecontainer is based on utilizing a range finder with pulsed laser ortriangulation, or ultra sound echo ranging.

In some examples, estimating the optical path length through thecontainer is based on utilizing a wall localization imaging method,wherein the wall localization imaging method is based on focusdetection, or spot detection or image analysis.

The disclosure also relates to a system of determining a concentrationof at least a first gas in a container having at least one flexible orvariable side or wall. The system comprises a light source fortransmitting a first light signal through the container and a detectorfor detecting transmitted light. The system further includes anestimation unit for estimating an unknown optical path length that thefirst light signal travels through the container and a control unit fordetermining the concentration of the at least first gas in the containerbased on detected light of the first light signal and the optical pathlength estimated by the estimation unit.

In some examples the estimation unit comprising a second light sourcefor transmitting a second light signal through a second gas with a knownconcentration over a known optical path length.

In some examples the control unit is further configured to estimate theunknown optical path length based on an absorption signal obtained bythe second light signal.

In some examples the system comprises a movable objective lens and thatthe objective lens, the detector and the light source and the estimationunit has a confocal configuration.

In some examples the estimation unit is a range finder with pulsed laseror triangulation, or ultra sound eco ranging.

In some examples the estimation unit is a wall localization system, andwherein the wall localization imaging system is based on focusdetection, or spot detection, or image analysis.

Examples

Three different examples of measurement solutions of oxygen sensinginside flexible packages were performed. These three experiments werecarried out to demonstrated increased performance regarding bothaccuracy and variation.

TABLE 1 New method Input sample Autosensing 0.63 3.65 Pulling 0.64 4.05Push 0.60 3.95 True Value 0.6 0.6

The studied sample was a bag of pasta. The oxygen content was measuredwith a reference technology to 0.6% O2, in good agreement with the lasertechnology results.

The laser is placed within the laser head, which makes it impossible toplace the bag firmly against the laser. This yields an offset since thelaser light has been passing through a 14 mm long column of air, with20.9 percent oxygen, before passing through the bag. The absorption dueto the distance between the laser and the end of the laser module isremoved from the obtained absorption signal.

Example of Pulling

The configuration was similar as to the configuration illustrated inFIG. 1. The laser head and detector were set a known distance apart(48.1 mm). To illustrate the improved performance of using a pullingtechnology, i.e. the sample walls in close contact to laser anddetector, two sets of measurements were performed.

In the first set the bag was randomly placed between the laser head anddetector and measured during one second without having the light sourcehead and detector head in contact with the container. In the second setthe bag was stretch out/pulled by external means to fill the voidbetween the light source head and detector head and also measured insimilar random position of the bag. 15 measurements with the bagrandomly placed and then stretched were made.

The results of the two measurement sets are presented in FIG. 10 in abox plot 500. A clear improvement of the accuracy and the variation ofthe measured values are obtained by positioning the walls with externalmeans, e.g. pulling 511 or using suction compared to not pulling 510.

FIG. 10 is demonstrating the improved performance of gas sensing as thesample walls are externally positioned close to the light source headand detector head. The sample oxygen content of the container was 0.6%O2.

Example of Pushing

The configuration was similar as to the configuration illustrated inFIG. 2. The light source head and detector head were set a knowndistance apart (64.3 mm). To illustrate the improved performance ofusing a pushing technology, i.e. the sample walls in close contact withthe light source head and detector head, two sets of measurements wereperformed.

In the first set the bag was randomly placed between the laser head anddetector and measured during one second.

In the second set the bag was pressed together at the bottom part sothat the top part would fill the space between the laser head anddetector. 15 measurements with the bag randomly placed and then pushedwere made.

The results of the two measurement sets are presented in FIG. 11 in abox plot 600. A clear improvement of the accuracy and the variation ofthe measured values are obtained by pushing 611 the walls to a closeproximity to the light source head and detector head compared to notpushing 610.

FIG. 11 is demonstrating the improved performance of gas sensing 611 asthe sample walls are pushed towards the light source head and detectorhead by pressing on the sample at another location. The sample oxygencontent of the container was 0.6% O2.

Example of Auto Sensing

Measurements were performed to illustrate the improved performance bymoving the laser and detector in close distance of the package walls andby detect the distance compared to having the laser and detector fixed.

The laser head and detector were set 64.7 mm apart. The detector wasthen moved in direction in order to close the distance to the laser headand then back to its original position. The distance between the laserhead and detector was re-measured. This procedure was repeated fivetimes and resulted in mean distance of 64.7 mm. For every measurementthe bag was randomly placed between the laser head and detector, in suchway that the bag was in contact with the laser head and measured duringone second. For the same random position the detector was moved indirection towards the laser head until it was in contact with the bag.The value was re-measured and the distance between the laser head anddetector was measured.

The results of the measurement are presented in FIG. 12 in a box plot700. A clear improvement of the accuracy and the variation of themeasured values are obtained when the laser and detector are moved intothe package and the distance is measured compared to if the package isplaced between the laser and detector with a fixed distance.

FIG. 12 demonstrating the improved performance of gas sensing as thelaser and detector are moved into close distance to the package wallsand the distance is measured (‘distance adjustment’) 711 compared tofixed positioned light source head and detector head (‘No adjustment’)710. The sample oxygen content of the container was 0.6% O2.

Example of Headspace Gas Analysis of Tray Package

In an example, the headspace gas in tray packages was analyzed. Traypackages with MAP consist of a rigid plastic tray that may betransparent or colored. To protect the food contents, the tray is filledwith a gas mixture and a plastic film is sealed around the edges of thetray. The plastic film is typically transparent or partiallytransparent. Often, the tray is filled with a slight overpressure sothat the top film bulges upward. The bulging is typically not welldefined, so there is a need to create a well-defined optical path lengthin the headspace in order to analyze the gas inside.

A gas measurement configuration is illustrated in FIGS. 13A and 13B. Theillustrated configuration 1300 works similarly to the exemplary devicedescribed in relation to FIGS. 2 and 3.

FIG. 13A illustrates a configuration 1300 comprising a light source1301, a detector in reflection configuration 1302. Alternatively, adetector in direct transmission configuration 1302′ may be used. Thesample is a tray 1303 (package) with a flexible protection 1307 being atleast partly transparent, such as a film. The configuration furthercomprises a mechanical means 1305 for pushing down the protective top1307, such as a foil, of the tray 1303. This mechanical mean 1305 is ameans for making contact between an exterior of the walls or sides ofthe container and thereby creating a determinable optical path lengththrough the container when contact is made. The configuration 1300 mayalso, in some examples, comprise a second mechanical means forpositioning the tray 1305.

FIG. 13B illustrates the same exemplary configuration as illustrated inFIG. 13A but from a side view. Light source 1301 and detector 1302 inreflection configuration. The detector 1302′ illiterates an alternativeconfiguration in transmission mode. In FIGS. 13A and 13B, a light beamis directed at an angle by a light source 1301 through a top film 1307of the tray 1303 and through a headspace at the sidewall 1306 of thetray 1303. This configuration ensures that the contents of the packagemay not interfere with the light beam. Depending on whether the sidewall1306 of the tray 1303 is transparent or not, either a detector inreflection mode 1302 or a detector in transmission mode 1302′ may beused. Alternatively, in the case the sidewall 1306 of the tray 1303 istransparent; a reflecting surface could be used instead of the detector1302′ (not illustrated).

In the illustrated example, the tray 1303 is positioned aided by anoptional mechanical device 1304 so that the position of the sidewall iswell defined. The assembly 1305 pushes down the top of the film 1307 toprovide a well-defined optical path inside the headspace between thelaser 1301 and the sidewall 1306. Thereby creating a well-definedoptical path length between the laser 1301 and the detector 1302, 1302′.

In some examples, the light source 1301 and detector 1302 aremechanically mounted on the mechanical device 1305.

FIG. 14 presents 100 actual measurements 1400 of O2 concentration inpercent in a tray using the described setup in relation to FIGS. 13A and13B. The tray had black sidewalls and transparent top film. The tray wasfilled with minced meat. Even though the tray was made of black plastic,there was sufficient diffuse reflection from the sidewall to provide auseful signal. While several examples of the present disclosure havebeen described and illustrated herein, those of ordinary skill in theart will readily envision a variety of other means and/or structures forperforming the functions and/or obtaining the results and/or one or moreof the advantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the presentdisclosure. More generally, those skilled in the art will readilyappreciate that all parameters, dimensions, materials, andconfigurations described herein are meant to be exemplary and that theactual parameters, dimensions, materials, and/or configurations willdepend upon the specific application or applications for which theteachings of the present disclosure is/are used. Also, different methodsteps than those described above, performing the method by hardware, maybe provided within the scope of the disclosure. The different featuresand steps of the disclosure may be combined in other combinations thanthose described. The scope of the disclosure is only limited by theappended patent claims.

The invention claimed is:
 1. A method of determining a concentration ofa gas in a headspace of a tray having a flexible protective layer, saidflexible protective layer and a surface of a content arranged on abottom surface of said tray which is at least partially defining saidheadspace, said method comprising: creating an optical path lengththrough said headspace of said tray by contacting and pushing saidprotective layer towards a bottom surface of said tray using amechanical fixture; transmitting a light signal only between a lightsource head and a detector head through said optical path length; theoptical path length is defined by either a length from a point of entryof light through the protective layer to a point of transmission througha transmitting wall of said tray, or from a point of entry of lightthrough the protective layer and from a point of reflection at areflective surface to a point of exit of light through the protectivelayer; determining said concentration of said gas in said headspace ofsaid tray based on detected transmitted light and said optical pathlength.
 2. The method of claim 1, comprising positioning one or more ofsaid light source head and said detector head against said protectivelayer.
 3. The method of claim 1, wherein said mechanical fixturecomprises one or more of said light source head and said detector head.4. The method of claim 1, comprising detecting when one or more of saidlight source head and said detector head is in contact with saidprotective layer, thereby estimating a distance of said optical pathlength between said light source head and said detector head.
 5. Themethod of claim 1, comprising utilizing a calibration routine based onusing two laser beams for determining said concentration.
 6. The methodof claim 1, comprising a calibration routine based on measurements on atleast a second tray having similar optical path length and a knownconcentration of said gas for determining said concentration.
 7. Themethod of claim 1, comprising positioning said light source head andsaid detector head at opposite sides of said optical path length; orpositioning said light source head and said detector head at the sameside of said optical path length and reflecting said light transmittedalong said optical path length in a content of said tray, or in an innersurface of said tray.
 8. The method of claim 1, wherein a light signalis transmitted at an angle by said light source through said protectivelayer and said headspace of said tray, and wherein said detector head isdetecting a signal being reflected by an inner surface, or transmittedthrough a wall of said tray.
 9. The method of claim 1, wherein adistance of said optical path length is estimated.
 10. The method ofclaim 9, wherein said distance of said optical path length is estimatedby using positions of said detector head or said light source head. 11.The method of claim 10 comprising using mechanical, or optical orelectronic means for estimating said position of said detector head orsaid light source head.
 12. The method of claim 1, wherein a distance ofsaid optical path length is estimated using a ranging method.
 13. Themethod of claim 12, wherein said distance of said optical path length isestimated using a ranging method selected from a group consisting of alaser range finder, a triangulation, and an ultra sound echo ranging; orwherein said distance of said optical path length is estimated using awall localization system selected from a group consisting of a walllocalization imaging system based on focus detection, spot detection,and an image analysis.
 14. The method of claim 1, comprising pushingdown said protective layer using said mechanical fixture.
 15. A systemfor measuring a concentration of a gas in a headspace of a tray having aflexible protective layer, said flexible protective layer and a surfaceof a content arranged on a bottom surface of said tray which is at leastpartially defining said headspace, said system comprises: a light sourcehead and a detector head; a mechanical fixture disposed adjacent to andoutside of said tray; said mechanical fixture applying downward force tosaid protective layer towards said bottom surface of said tray therebycreating an optical path length through said headspace of said tray; theoptical path length defined by either a length from a point of entry oflight through the protective layer to a point of transmission through atransmitting wall of said tray, or from a point of entry of lightthrough the protective layer and from a point of reflection at areflective surface to a point of exit of light through the protectivelayer; a control unit for determining said concentration of a gas insaid headspace of said tray based on detected light and said opticalpath length upon said contact.
 16. The system of claim 15, comprisingone or more of means for estimating a distance of the optical pathlength by using positions of said detector head and said light sourcehead.
 17. The system of claim 15, comprising means for estimating adistance of the optical path length by using a ranging method.
 18. Thesystem of claim 15, comprising means for estimating a distance of theoptical path length using a wall localization system.
 19. The system ofclaim 15, wherein said mechanical fixture comprises one or more of saidlight source head and said detector head.
 20. The system of claim 15,further comprising one or more of the following: wherein said lightsource head is configured for transmitting light at an angle throughsaid headspace of said tray, and wherein said detector head isconfigured for detecting a signal being reflected by said inner surface,or transmitted through a wall of said tray; wherein said light sourcehead and said detector head is positioned at opposite sides of saidoptical path length; and wherein said light source head and saiddetector head is positioned at the same side of said optical path lengthand configured for reflecting light transmitted along said optical pathlength in a content of said tray, or in an inner surface of said tray.21. The system of claim 15, comprising means for estimating a distanceof the optical path length by detecting when said mechanical fixture isin contact with said protective layer, thereby estimating a distance ofsaid optical path length between said light source head and saiddetector head.
 22. The system of claim 15, comprising means forestimating a distance of the optical path length by using a rangingmethod selected from a group consisting of a laser range finder, atriangulation, and an ultra sound echo ranging.
 23. The system of claim15, comprising means for estimating a distance of the optical pathlength using a wall localization system selected from a group consistingof a wall localization imaging system based on focus detection, a spotdetection, and an image analysis.
 24. A method of determining aconcentration of a gas in a headspace of a tray having a flexibleprotective layer, said flexible protective layer and a surface of acontent arranged on a bottom surface of said tray which is at leastpartially defining said headspace, said method comprising: creating anoptical path length through said headspace of said tray by contactingand pushing said protective layer towards a bottom surface of said trayusing a mechanical fixture; transmitting a light signal only between alight source head and a detector head through said optical path length;the optical path length extending only between either 1) a length from apoint of entry of light through the protective layer to a point oftransmission through a transmitting wall of said tray, or 2) from apoint of entry of light through the protective layer and from a point ofreflection at a reflective surface to a point of exit of light throughthe protective layer; determining said concentration of said gas in saidheadspace of said tray based on detected transmitted light and saidoptical path length.